1. Field of the Invention
The present invention relates to an exhaust gas recirculation valve (hereinafter referred to as "EGR valve") driven by an electric motor. More particularly, it relates to an EGR valve adapted to operate so as to give a determined optimum amount of exhaust gas recirculation (hereinafter referred to as "EGR") necessary for emission control, the operation thereof being independent of the influence of mainfold vacuum.
2. Description of the Prior Art
Most of conventional EGR valves, as found for instance in U.S. Pat. Nos. 4,066,056 and 4,090,482, are provided in the upper portion of their valve housing with a diaphragm chamber connected to an engine manifold, and are adapted to be opened and closed by manifold vacuum introduced into said diaphragm chamber by some means or other. In these EGR valves, an opening thereof suitable for an engine load is obtained by elaborated means of introducing manifold vacuum into said diaphragm chamber. However, when a larger opening of the valve is necessary, the vacuum itself is reduced. On the other hand, when a very small opening thereof is necessary, the vacuum becomes too high. Thus, the conventional EGR valves have the disadvantage that the opening thereof has to be controlled under such incompatible conditions.